1. Technical Field
The present invention relates to a cordless telephone system such as a wireless private automatic branch exchange (PABX) or a key phone system providing a radio communication service, and more particularly, to a method for synchronizing a frame number, a multi-frame numbs and a primary scan carrier number (PSCN) of every base stations in a DECT (Digital European Cordless Telecommunications) cordless telephone system.
2. Related Art
Initially, DECT was intended mainly to be a private system, to be connected to a private automatic branch exchange (PABX) to give users mobility, within PABX coverage, or to be used as a single cell at a small company or in a home. As the idea with telepoint was adopted and generalized to public access, DECT became part of the public network. DECT was created to interface seamlessly to existing and future fixed networks such as public switched telephone network (PSTN), integrated services digital network (ISDN), global system for mobile communication (GSM), and PABX. DECT cordless telephone systems can be classified in three groups according to use, first as residential cordless telephone system used in residential districts, then as public cordless telephone systems, and lastly, as business cordless telephone systems used in office buildings. A particular example of such cordless telephone systems is the Second Generation Cordless System (CT2) with digital common air interface (CAI) specification. CT2 cordless telephone systems provide radio communication services by using frequency division multiple access (FDMA)/time division multiplex (TDD). However, current CT2 cordless telephone systems do not provide an effective inter-cell handover, and in case of using a single antenna, need a combiner/divider.
DECT cordless telephone systems employ standard radio connection technique specified by the European Telecommunications Standards Institute (ETSI) to provide radio communication services based on time division multiple access (TDMA)/time division duplex (TDD). In its simplest form, each DECT system has a base station with at least one mobile unit. More complex systems contain several base stations each having several mobile units. Exemplars of contemporary DECT systems are disclosed in detail in ETS 300 175-1 to 175-9, EP 0 486 089, entitled "Effective Carrier Scanning Method in Terminal", EP 0 445 887, entitled "Method for Optimizing Beacon Message in Base Station", EP 0 587 225, entitled "Method for Transmitting Data to DECT Communication Channel."
Such DECT cordless telephone systems perform radio connection based on the standards specified by ETSI as follows:
Frequency Band: 1880-1900 MHz PA1 Number of Carriers: 10 PA1 Carrier Spacing: 1.728 MHz PA1 Peak Transmit Power: 250 mW PA1 Carrier Multiplex: TDMA (24 slots per frame) PA1 Frame Length: 10 ms PA1 Basic Duplexing: TDD using 2 slots on same RF carriers PA1 Gross Bit Rate: 1152 kbit/s PA1 Net Channel Rates:
32 kbit/s (B-field per slot) PA2 6.4 kbit/s (control/signaling per slot)
Generally, base station of the DECT cordless telephone system provides a 10 msec synchronization pulse to synchronize DECT bursts for effective inter-cell handover operations. Contemporary techniques for the synchronization of base stations in such a cordless telephone system are disclosed, for example, in U.S. Pat. No. 5,329,635 for Seamless Handoff For Radio Telephone Systems issued to Wadin et al., U.S. Pat. No. 5,347,562 for Synchronizing Groups Of Base Stations In Time Division Duplex Communication Systems issued to Candy, U.S. Pat. No. 5,396,541 for Call Handoff In A Wireless Telephone System issued to Farwell et al., U.S. Pat. No. 5,473,668 for Digital Cordless Telephone System Readily Capable Of Setting Up issued to Nakahara, U.S. Pat. No. 5,519,759 for Method For The Synchronization Of Base Stations In A Multicellular, Wireless Telephone System issued to Heineck et al., U.S. Pat. No. 5,625,888 for Process For Combining Transmitting/Receiving Devices Of A Cordless Communication System To Form A Communicating Unit issued to Ruther et al., and U.S. Pat. No. 5,666,366 for Inter-Base Synchronization Technique For A TDMA Communication System issued to Malek et al. However, I have observed that the frame number, the multi-frame number, and the primary scan carrier number (PSCN) of the respective base stations are not synchronized. As a result, inter-cell handover may not be effectively managed.